Existing windmills with a horizontal axis and of the propeller type, and also of the egg-beater type with vertical axis and arranged for generating electricity, require a speed-up transmission. It is not uncommon to use a speed-up transmission having a ratio of 40 to 1 for driving an electric generator at around an optimum speed of 2,000 to 3,000 r.p.m., using a windmill rotating at about 50 r.p.m. Such transmissions are expensive to make, require considerable maintenance, often break down and considerably decrease the overall efficiency of the wind electric generator.